Engine air flow can be affected by engine system components on both the intake side and the exhaust side of engine cylinders. For example, engine exhaust manifolds can affect exhaust back pressure, cylinder mixture, and engine emissions. On the other hand, charge motion control valves, variable cam timing devices, and intake manifold design can affect engine air flow from the intake side of engine cylinders. If the engine system provides increased exhaust back pressure, engine efficiency may decrease while engine emissions may increase. In U.S. Pat. No. 5,822,986, an engine system having exhaust manifolds that separate cylinder exhaust discharge between engine cylinders by 270 or more crankshaft degrees is disclosed. This engine system purports to reduce exhaust gas interference between engine cylinders.
The above-mentioned method can also have several disadvantages. Specifically, the system applies to a four-stroke V-eight engine that has a firing order of 1-3-7-2-6-5-4-8. However, the firing order may not be perceived as smooth as other firing orders. Further, the exhaust manifold may not function as well with engines having different firing orders that may be perceived as smoother. Further still, the described exhaust manifold may only provide improved engine performance and emissions in a limited engine operating range.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine system for improving engine fuel economy, performance, and emissions.
One example of the present description includes an engine system, comprising: an exhaust manifold including a first Y-pipe, said first Y-pipe including a first pipe and a second pipe, said first pipe and said second pipe coupled to a confluence pipe, said first pipe extending to solely engage exhaust ports of first and second cylinders of an engine cylinder bank, said second pipe extending to solely engage exhaust ports of third and fourth cylinders of said engine bank, said first and second cylinders 90 crankshaft degrees apart in an engine firing order.
By closely coupling the exhaust of cylinders that are 90 crankshaft degrees apart in an engine firing order, it is possible to reduce engine exhaust back pressure and improve engine air flow for engines having combustion orders that may be perceived smoother. Further, engine emissions may be reduced because exhaust gases from cylinders that are close in an engine firing may take a more direct path to an engine after treatment device. Consequently, engine emissions may be reduced by earlier activation of exhaust after treatment devices.
In another example, the present description provides for an engine system, comprising: an engine including a camshaft with at least one intake valve lobe having an intake valve opening duration of at least 260 crankshaft degrees; and a mid-position locking camshaft phasor coupled to said camshaft and configured to adjust a cam timing of a cylinder bank of said engine; and an exhaust manifold coupled to said engine and including a first Y-pipe, said first Y-pipe including a first pipe and a second pipe, said first pipe and said second pipe coupled to a confluence pipe, said first pipe extending to solely engage exhaust ports of first and second cylinders of said engine cylinder bank, said second pipe extending to solely engage third and fourth cylinders of said engine bank, said first and second cylinders 90 crankshaft degrees apart in an engine firing order.
Engine air flow and emissions can be improved by an engine system that synergistically combines cylinder intake air control with an exhaust manifold that lowers exhaust back pressure. In particular, charge motion control valves and variable cam timing can improve engine breathing when an exhaust system can combine exhaust from engine cylinders that are separated by 90 crankshaft degrees in an engine combustion order.
The present description may provide several advantages. In particular, the approach may improve engine performance by lowering exhaust backpressure for an engine having a different firing order. Further, the present description may improve engine emissions by increasing heat flux to engine after treatment devices during an engine start. Further still, the present description may provide improved engine performance over a wider engine operating range.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.